[gitg] Fix side-by-side alignment in the case of a single image

[Jesse van den Kieboom <jessevdk src gnome org>]

commit c0c44a95639175675f46943ccd9b0a6b9933927b
Author: Jesse van den Kieboom <jessevdk gnome org>
Date:   Mon Aug 29 05:43:06 2016 +0200

    Fix side-by-side alignment in the case of a single image

 libgitg/gitg-diff-image-side-by-side.vala |   10 ++++++++--
 1 files changed, 8 insertions(+), 2 deletions(-)
---
diff --git a/libgitg/gitg-diff-image-side-by-side.vala b/libgitg/gitg-diff-image-side-by-side.vala
index 4e15240..254b25e 100644
--- a/libgitg/gitg-diff-image-side-by-side.vala
+++ b/libgitg/gitg-diff-image-side-by-side.vala
@@ -237,10 +237,16 @@ class Gitg.DiffImageSideBySide : Gtk.DrawingArea
                ctx.render_background(cr, alloc.x, alloc.y, alloc.width, alloc.height);
 
                double max_height = double.max(sizing.old_size.image_height, sizing.new_size.image_height);
+               double spread_factor = 0.5;
+
+               if (old_surface != null && new_surface != null)
+               {
+                       spread_factor = 2.0 / 3.0;
+               }
 
                if (old_surface != null)
                {
-                       var x = (sizing.old_size.width - sizing.old_size.image_width) * 2 / 3;
+                       var x = (sizing.old_size.width - sizing.old_size.image_width) * spread_factor;
                        var y = (max_height - sizing.old_size.image_height) / 2;
 
                        cr.set_source_surface(old_surface, x, y);
@@ -258,7 +264,7 @@ class Gitg.DiffImageSideBySide : Gtk.DrawingArea
 
                if (new_surface != null)
                {
-                       var x = (sizing.new_size.width - sizing.new_size.image_width) * 1 / 3;
+                       var x = (sizing.new_size.width - sizing.new_size.image_width) * (1.0 - spread_factor);
                        var y = (max_height - sizing.new_size.image_height) / 2;
 
                        if (cache.old_pixbuf != null)